Refrigeration apparatus and method

ABSTRACT

Methods and apparatus for an energy efficient freezer or cooler defrost, which are particularly suited for an automated system, include procedures utilized for this purpose. The procedures are included in the firmware of an embedded controller and operate the cooler or freezer defrost cycle when required for increased energy efficiency.

CROSS-REFERENCED APPLICATIONS

This application claims priority to U.S. Provisional Application Ser. No. 61/566,555, filed on Dec. 2, 2011, which is incorporated herein in its entirety by reference thereto.

BACKGROUND

1. Field of the Disclosure

This disclosure generally relates to a refrigeration apparatus and method and, in particular, to a refrigeration apparatus and method for efficient defrost of an evaporator assembly.

2. Discussion of the Background Art

In the current economic climate and legislative arena there is a necessity to reduce the energy consumption of HVAC and refrigeration equipment. To reduce the overall energy consumption of this equipment, electronic controllers are being applied to optimize the energy consumption of such equipment. One function that requires optimization is evaporator defrost.

Prior art defrost strategies have used a timer to initiate a defrost process based on a predetermined schedule, whether or not needed. For the case of not needed, there is an unnecessary consumption of energy. The process of defrosting introduces heat into the conditioned air space, making energy saving important (i) to reduce the amount of energy used to defrost, and (ii) to reduce the additional energy required to remove the defrost heat from the conditioned air space.

Thus, there is a need for a refrigeration apparatus and method that initiates a defrost only when needed.

SUMMARY OF THE DISCLOSURE

A refrigeration apparatus according to the present disclosure comprises a fan that provides an airflow, an evaporator assembly that comprises an evaporator coil disposed in the airflow, and a refrigerant assembly disposed in fluid communication with the evaporator coil to supply refrigerant to the evaporator coil. A first sensor that senses a temperature of the airflow at an airflow input side of the evaporator coil and a second sensor that senses a temperature of the airflow at an airflow output side of the evaporator coil. A third sensor that senses the temperature on the suction line near the outlet of the evaporator coil. A fourth sensor that senses the temperature in a location that is representative of the evaporator coil surface temperature. A fifth sensor (pressure transducer) that senses the pressure of the refrigerant leaving the evaporator coil. A controller is connected to the first, second, third, fourth and fifth sensors to control the evaporator assembly and the refrigerant assembly in a cooling mode and in a defrost mode. The controller controls an initiation of the defrost mode based on comparison of a reference dynamic efficiency with a dynamic efficiency that is a function of current values of the input airflow temperature, the output airflow temperature and an output saturated refrigerant temperature of the refrigerant leaving the evaporator coil. The controller controls the termination of the defrost mode based on the temperature value sensed by the fourth sensor satisfying a temperature setting value within the defrost program or by time based on satisfying a time setting within the defrost program. The defrost mode terminates when the temperature setting or time setting has been satisfied (first achieved).

A method for efficient defrosting of an evaporator assembly, the method comprising: (a) Initiating start up of a refrigeration assembly, fan motor and fan if Tair, in is greater than a temperature set point; (b) Cooling Tair, in to within a predetermined temperature setting relevant to a thermostat set point; (c) Initiating a defrost program if Tair, in is within a predetermined range of the thermostat set point; (d) Calculating reference dynamic efficiency (RE) and dynamic efficiency (DE) values; (e) Determining if RE minus DE divided by RE is equal to a predetermined threshold (DET) and if yes, then initiating an electric defrost by deactivating the refrigeration assembly, deactivating the fans and activating at least one defrost heater; (f) Determining if (a) a temperature sensed by a defrost termination sensor is equal to or greater than preset defrost termination temperature, (b) a defrost time is equal to or greater than a preset defrost termination time, or (c) a evaporator coil temperature is equal to or greater than a heater safety termination temperature; and (g) If any one of (a)-(c) in step (f) occur, deactivating the defrost heater, activating the refrigeration assembly and activating the fans.

BRIEF DESCRIPTION OF THE DRAWINGS

Other and further objects, advantages and features of the present disclosure will be understood by reference to the following specification in conjunction with the accompanying drawings, in which like reference characters denote like elements of structure and:

FIG. 1 is a block diagram of a refrigeration apparatus according to the present disclosure;

FIG. 2 is a block diagram that depicts components of the refrigeration apparatus of FIGS. 1; and

FIG. 3 is a flow diagram of the programs of FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1, a refrigeration apparatus 20 of the present disclosure comprises an evaporator assembly 22, a refrigerant assembly 24 and a controller 26.

Evaporator assembly 22 is located in an enclosed space 28 that requires refrigeration or air conditioning. Refrigerant assembly 24 and controller 26 are located outside enclosed space 28 with connections to one another and to evaporator assembly 22. Enclosed space 28 may be a room that is being cooled for refrigeration or air conditioning. For example, in a preferred embodiment, enclosed space 28 is a walk in refrigeration room.

Evaporator assembly 22 comprises a cabinet 29 that has openings 31 and 33 located in opposed sidewalls. Disposed within cabinet 29 are an evaporator coil 30, one or more defrost heater(s) 32, one or more fan(s) 34 and one or more fan motor(s) 36. Refrigerant enters cabinet 29 via a liquid line 40 and leaves via a compressor suction line 42. Lines 40 and 42 are connected to refrigerant assembly 24. Air flows through cabinet 29 via openings 31 and 33 as indicated by arrows 44 and 46. Defrost heater 32 comprises one or more heating elements (not shown).

During a cooling mode, controller 26 operates refrigerant assembly 24 to flow refrigerant through liquid line 40, refrigerant metering device 48 typically an electric expansion valve or mechanical expansion valve, evaporator coil 30 and suction line 42. Controller 26 also operates fan motor 36 to rotate fan 34 to draw air from enclosed space 28 via opening 31 through evaporator coil 30 by fan 34. As the air passes through evaporator coil 30, heat is removed from the air and transferred to the colder refrigerant flowing through evaporator coil 30. That is, air is cooled and moved by fan 34 into enclosed space 28 via opening 33. The net effect is that the air in enclosed space 28 is cooled.

Evaporator coil (heat exchanger) 30 is constructed such that the refrigerant and airflow pass through the evaporator coil without the two mediums coming physically into contact. For example, evaporator coil 30 is constructed with a tube through which the refrigerant flows, the tube being arranged as evaporator coil 30. Evaporator coil 30 facilitates heat transfer from the air to the refrigerant.

Enclosed space 28 generally requires access by a user that results in warm moist/humid air being introduced to enclosed space 28. The moisture in the infiltrating air or from the product stored inside enclosed space 28 will be attracted to the cold surfaces within the enclosed space. Since the evaporator coil surfaces are the coldest surfaces in enclosed space 28 and exposed to a higher airflow rate than any other surfaces in enclosed space 28, when the fan(s) 34 circulate the air through the evaporator coil 30, the moisture in the air is deposited on the evaporator coil surfaces.

The ice deposits on evaporator coil 30 impede the performance of evaporator assembly 22 in two ways. First, the ice on the fins (not shown) of evaporator coil 30 acts as an additional insulative barrier between the airflow and the refrigerant; thereby reducing heat transfer from the air to the refrigerant. Second, the ice constricts the airflow through evaporator coil 30, thereby causing reduced airflow. To remove the ice deposits and maintain the design performance efficiency of evaporator assembly 22, defrosting is required. A defrost mode may be activated by one of three methods:

-   -   Demand Defrost Mode (primary active defrost mode)—a demand         defrost automatically initiated based on operating efficiency         status of evaporator.         -   Safety Defrost Mode—a safety defrost automatically initiated             (if actively programmed) if applicable preprogrammed             parameters have been satisfied.         -   Manual Defrost Mode—a manual defrost can be manually             initiated via the controller interface.

During a defrost mode, controller 26 operates defrost heater 32 to melt the ice. Defrost heater 32 is embedded in, attached to or in close proximity to evaporator coil 30 and the air heat transfer surfaces of evaporator coil 30. During defrost the surfaces of evaporator coil 30 are heated to above the freezing point of the ice. As a result the ice melts into a liquid that is removed from enclosed space 28 via an evaporator drain (not shown).

Evaporator assembly 22 further comprises an input air temperature sensor 50, an output air temperature sensor 52, an evaporator output refrigerant temperature sensor 82, a defrost termination sensor 84, 92, a heater safety termination (HSTS) switch 68 and a refrigerant suction pressure transducer (sensor) 86. Input air temperature sensor 50 is disposed in the airflow at or near an input port of evaporator assembly 22 or of evaporator coil 30. Output air temperature sensor 52 is disposed in the airflow at or near an output port of evaporator coil 30 or of evaporator assembly 22. The output signals of input air and output air temperature sensors 50 and 52 are labeled, respectively, Tair, in (50, 56) and Tair, out (52, 58) and are proportional to the input airflow and output airflow temperatures, respectively. Refrigerant suction pressure transducer (sensor) 86 is located to measure the pressure of the refrigerant that exits evaporator coil 30. The output signal of refrigerant suction pressure transducer (sensor) 86, 88 is labeled Tref, out and can be used to determine the output saturated refrigerant temperature in evaporator coil 30.

Evaporator output temperature sensor 82 is located adjacent to and in contact with suction line 42 at or near its connection to the output side of evaporator coil 30. Defrost termination sensor 84 is located on the evaporator coil 30. HSTS sensor 68 is a safety switch which opens or closes based on coil temperature and is located on evaporator coil 30.

Referring to FIG. 2, controller 26 comprises a processor 70, a memory 74 and an input/output (I/O) interface 72 that are interconnected by a bus 76. Memory 74 comprises programs that are executed by processor 70 to operate refrigeration apparatus 20. Germane to the present disclosure are a cooling program 78 and a defrost program 80. Although shown as separate programs, defrost program 80 in some embodiments may be incorporated within cooling program 78.

Processor 70 may be any suitable processor that executes or runs the programs stored in memory 74. For example, processor 70 may be a microprocessor.

Memory 74 may be any suitable memory that stores the parameters and data required for operation and maintenance of refrigeration apparatus 20. For example, memory 74 may comprise one or more of a random access memory, a read only memory, an EPROM, a plug in memory such as a flash memory or a data key, and the like.

I/O (input/output) interface 72 is further connected to input air temperature sensor 50, output air temperature sensor 52, fan motor 36, defrost heater 32, refrigerant assembly 24, a refrigerant pressure transducer 86, an output refrigerant temperature sensor 82, a defrost termination sensor 84, and an HSTS switch 68 via connections 56, 58, 62, 64, 66, 88, 90, 92 and 96, respectively.

Processor 70 executes cooling program 78 in a cooling mode to cause refrigerant assembly 24 to flow refrigerant through liquid line 40, a refrigerant metering device 48 (such as an electric expansion valve or mechanical expansion valve), evaporator coil 30 and suction line 42. Processor 70 also operates fan motor 36 to rotate fan 34 to draw air via opening 31 from enclosed space 28 through evaporator coil 30 by fan 34 as indicated by arrow 44. As the air passes through evaporator coil 30, heat is removed from the air and transferred to the colder refrigerant flowing through evaporator coil 30. That is, air is cooled and moved by fan 34 via opening 33 into enclosed space 28 as indicated by arrow 46. The net effect is that the air in enclosed space 28 is cooled.

As noted above, warm moist/humid air introduced to enclosed space 28 causes a deposit of ice on cold surfaces in the enclosed space 28. These ice deposits will be most prominent at the surfaces of evaporator coil 30, which are the coldest surfaces in enclosed space 28 and exposed to a higher airflow rate than any other surfaces in enclosed space 28.

While cooling program 78 is being executed, processor 70 frequently checks the temperature values of Tair, in, Tair, out and Tref, out for a predetermined temperature condition based on at least one and, preferably more of these temperatures, that requires an initiation of a defrost mode. For example, the checking operation is an initial step of defrost program 80. If the temperature condition does not require defrost, processor 70 continues to execute cooling program 78.

If the temperature condition requires defrost, processor 70 initiates defrost program 80. Processor 70 then, if refrigeration apparatus 20 is configured in an electric defrost mode, causes fan motor 36 to be turned off, defrost heater 32 to be turned on and refrigerant assembly 24 to discontinue supplying refrigerant to evaporator coil 30. If refrigeration apparatus 20 is configured in an air defrost mode, processor 70 causes refrigerant assembly 24 to discontinue supplying refrigerant to evaporator coil 30 for a predetermined period of time and also causes the fan(s) 34 to continue operating and circulating air through the evaporator coil surfaces.

Defrost program 80 in a preferred embodiment determines the temperature condition based on a dynamic effectiveness (DE) of the performance of a heat exchanger (evaporator coil 30). DE is defined as the actual heat transfer of a heat exchanger divided by the maximum amount of heat that could be transferred for the same inlet temperature and flow rates in both cases. For the evaporator where the refrigerant flow has a greater “heat capacity” than the air flow the effectiveness (E) can be expressed as the ratio:

E=(Tair,in−Tair,out)/(Tair,in−Tref,out),   (1)

where Tair, in is the temperature of the air entering evaporator coil 30, Tair, out is the temperature of the air exiting evaporator coil 30, and Tref, out is the saturated refrigerant temperature exiting evaporator coil 30.

Processor 70 executes defrost program 80 to monitor Tair, in, Tair, out and Tref, out to determine dynamic effectiveness DE. Tref, out is determined by looking up the saturation temperature that corresponds to a measured refrigerant pressure. A pressure transducer 86 measures the refrigerant pressure.

Each time processor 80 monitors Tair, in, Tair, out and Tref, out during execution of defrost program 80, the value of E is calculated by processor 70.

In the following description of defrost program 80 and FIG. 3, the following acronyms are used:

-   -   DE Dynamic Effectiveness     -   RE Reference Effectiveness     -   DET Defrost Effectiveness Threshold     -   DTT Defrost Termination Temperature     -   DTS Defrost Termination Sensor Temperature     -   DT Defrost Time     -   DETT Defrost Termination Time     -   HSTS Heater Safety Termination Switch     -   HSTT Heater Safety Termination Temperature

DET is a temperature value determined by design and user requirements. In one embodiment, DET is 35%. DTT is the predetermined defrost termination temperature that is found through testing, for example, typically 40-55° F. DETT is the amount of time that the defrost cycle operates if the defrost cycle is terminated by time.—HSTT is the coil temperature that cannot be exceeded, for example, 70° F. in one embodiment.

Referring to FIG. 3, processor 70 executes instructions of cooling program 78 to control start up of refrigeration apparatus 20 at box 100 by determining if Tair, in is greater than a temperature set point. If not, refrigerant assembly 24 is not started.

If yes, processor 70 initiates start up of refrigerant assembly 24, fan motor 36 and fan 34. Once start up begins, there is a delay at box 102 while processor 70 waits until Tair, in is cooled to within a predetermined programmed temperature setting (in one embodiment 15° F.) relevant to the thermostat set point before initiating defrost program 80. The temperature set point and thermostat set point are identical and are determined by the end user for the product that is being placed in enclosed space 28.

Once Tair, in is within 15° F. of the thermostat set point, processor 70 executes instructions of defrost program 80. At box 104 processor 70 executes instructions to start collecting data and calculations are initiated to establish RE and DE values. In one embodiment, the RE and DE values are initially both set to equal 0. Initially, DE will equal RE and DE will continue to equal RE until a peak RE value has been established. The peak RE value may change based on system operation as the system continues to operate and DE will also change accordingly. Once the final peak RE value is established (DE will equal RE) then the efficiency of the evaporator coil starts to deteriorate, the DE value will start to drop below the RE value.

At box 106 processor 70 executes instructions using equation (1) to calculate RE and DE in real time during operation of refrigeration apparatus 20. This calculation uses the current values of Tair, in, Tair out and Tref, out provided by input air temperature sensor 50, output air temperature sensor 52 and pressure transducer (sensor) 86. The processor 70 processes the collected real time data calculations and then per defrost program 80 instructions, generates RE and DE values. At box 108 processor 70 determines if the current processed value of DE is equal to RE. If yes, in box 110 DE is set equal to the current value of RE, which is used for the next comparison in box 108. Processor 70 then returns to box 104.

If no, at box 112 processor 70 determines if RE—DE divided by RE is equal to the predetermined threshold DET. If no, defrost program 80 returns to box 106.

If yes, control program 80 proceeds to either an electric defrost mode or an air defrost mode dependent on the system requirements or application, wherein refrigeration assembly is deactivated 116, evaporator fans are deactivated 116A and defrost heaters are activated 118 for electric defrost mode or refrigeration assembly is deactivated 136 and evaporator fans continue to operate 138 for air defrost mode.

If refrigeration apparatus 20 is configured for an electric defrost mode, at box 116 refrigerant assembly 24 is disabled. That is, refrigerant is not supplied to evaporator coil 30. At box 116A controller 26 deactivates or turns off fan motor 36 and fan 34. At box 118 controller 26 activates or turns on defrost heater 32.

At box 120 processor 70 uses the temperature sensed by DTS sensor 84 to determine if it is equal to or greater than the defrost termination temperature DTT. If no, at box 122 processor 70 determines if the defrost time DT is equal to or greater than the defrost termination time DETT. If no, at box 124 processor 70 determines if the evaporator coil temperature is equal to or greater than the heater safety termination temperature HSTT. If no, cooling program 80 returns to box 120. If the determination at any of boxes 120, 122 or 124 is yes, at box 126 processor 70 causes controller 26 to deactivate defrost heater 32. At box 128 processor initiates a time delay to allow a “drip time” for the evaporator coil 30. When the delay has ended, refrigerant assembly 24 is activated, box 130. At box 132 a time delay is then initiated. When the time delay has ended, at box 134 processor 70 causes controller 26 to turn fan motor 36 and fan 34 on. Processor 70 then resumes execution of defrost program 80 at box 104.

If refrigeration apparatus 20 is configured for an air defrost mode, at box 136 refrigerant assembly 24 is deactivated. At box 138 processor 70 allows continued operation of fan motor 36 and fan 34. At box 140 processor 70 determines if DT is equal to or greater than DTT. If no, processor 70 continues to execute the instructions of box 140 until DT is equal to or greater than DTT. When this happens, at box 142 processor 70 causes controller 26 to activate refrigerant assembly 24 in box 142 to provide refrigerant flow to evaporator assembly 22. Processor 70 then resumes execution of defrost program 80 at box 104.

If refrigeration apparatus 20 is configured for a manual defrost mode 114, the method determined in 114A if a manual defrost has been requested. If no, then no defrost is initiated 114B. If yes, then defrost is initiated 115 and electric defrost procedures are followed in steps 116-142 as discussed above or air defrost procedures are followed in steps 136-142 as discussed above.

The method also provides for a safety defrost mode 113, wherein the system monitors various safety defrost parameters 113A to determine if the maximum safety defrost parameters are exceeded 113B. If parameters are not exceeded, then the system returns to 113A. If the parameters are exceeded, then the system initiates defrost 115 and electric defrost procedures are followed in steps 116-142 as discussed above or air defrost procedures are followed in steps 136-142 as discussed above.

There are several advantages to the electronic controller of the present disclosure. There is a cost saving, as energy costs increase the additional cost of the electronic controller becomes more justifiable. In a “smart kitchen concept” where all of the operating parameters are centralized in one microprocessor, the electronic controller of the present disclosure in refrigeration equipment is essential to communicate with a central microprocessor. There is also a legislative advantage as the electronic controller is able to collect and store temperature data, allowing a storeowner to prove correct storage temperature and conditions of food produce. The refrigeration apparatus of the present disclosure also has the advantage of initiating defrost when the conditions at the evaporator coil require defrost.

The present disclosure having been thus described with particular reference to the preferred forms thereof, it will be obvious that various changes and modifications may be made therein without departing from the spirit and scope of the present disclosure as defined in the appended claims. 

What is claimed is:
 1. A refrigeration apparatus comprising: a fan that provides an airflow; an evaporator assembly that comprises an evaporator coil disposed in said airflow; a refrigerant assembly disposed in fluid communication with said evaporator coil to supply refrigerant to said evaporator coil; a first sensor that senses a temperature of said airflow at an airflow input side of said evaporator coil; a second sensor that senses a temperature of said airflow at an airflow output side of said evaporator coil; a third sensor that senses a temperature on a suction line near the outlet side of said evaporator coil; a fourth sensor that senses a temperature in a location that is representative of an evaporator coil temperature; a fifth sensor that senses pressure of said refrigerant leaving said evaporator coil, wherein said pressure of said refrigerant corresponds to an output saturated suction refrigerant temperature; and a controller that is connected to said first, second, third, fourth and fifth sensors, that controls said evaporator assembly and said refrigerant assembly in a cooling mode and in a defrost mode, and that controls an initiation of said defrost mode based on comparison of a reference dynamic efficiency with a dynamic efficiency that is a function of current values of said temperature of said airflow at said airflow input side of said evaporator coil, said temperature of said airflow at said airflow output side of said evaporator coil and said output saturated suction refrigerant temperature of said refrigerant leaving said evaporator coil.
 2. The refrigeration apparatus of claim 1, wherein said evaporator assembly is disposed in an enclosed space that requires refrigeration and/or air conditioning.
 3. The refrigeration application of claim 2, wherein said refrigerant assembly and said controller are located outside said enclosed space.
 4. The refrigeration apparatus of claim 1, wherein said dynamic efficiency is determined by a difference between the current temperature values sensed by said first and second sensors divided by a difference between the temperature value sensed by said first sensor and said output saturated suction refrigerant temperature value sensed by said fifth sensor.
 5. The refrigeration apparatus of claim 1, wherein said first sensor is an input air temperature sensor.
 6. The refrigeration apparatus of claim 1, wherein said second sensor is an output air temperature sensor.
 7. The refrigeration apparatus of claim 1, wherein said third sensor is an evaporator output refrigerant temperature sensor.
 8. The refrigeration apparatus of claim 1, wherein said fourth sensor is a defrost termination sensor.
 9. The refrigeration apparatus of claim 1, wherein said fifth sensor is a refrigerant suction pressure transducer.
 10. The refrigeration apparatus of claim 1, further comprising a heater safety termination switch.
 11. The refrigeration apparatus of claim 1, wherein said heater safety termination switch is a safety switch which opens or closes based on said evaporator coil temperatures sensed by said heater safety termination switch and is located on said evaporator coil.
 12. A method for efficient defrosting of an evaporator assembly, said method comprising: a. Initiating start up of a refrigeration assembly, fan motor and fan if Tair, in is greater than a temperature set point; b. Cooling Tair, in to within a predetermined temperature setting relevant to a thermostat set point; c. Initiating a defrost program if Tair, in is within a predetermined range of said thermostat set point; d. Calculating reference dynamic efficiency (RE) and dynamic efficiency (DE) values; e. Determining if RE minus DE divided by RE is equal to a predetermined threshold (DET) and if yes, then initiating an electric defrost by deactivating said refrigeration assembly, deactivating said fans and activating at least one defrost heater or initiating an air defrost by deactivating said refrigeration assembly and maintaining continued operation of said evaporator fans; f. Determining if (a) a temperature sensed by a defrost termination sensor is equal to or greater than preset defrost termination temperature, (b) a defrost time is equal to or greater than a preset defrost termination time, or (c) a evaporator coil temperature is equal to or greater than a heater safety termination temperature; and g. If any one of (a)-(c) in step (f) occur, deactivating said defrost heater, activating said refrigeration assembly and activating said fans. 